Requirements exist for a unique type of underwater acoustic source. The transducer is in the form of a linear array of discrete elements and is required to have a constants transmitting voltage response and carefully controlled directivity characteristics over a two octave bandwidth. A generalized model of a linear array of cylindrical piezoelectric ceramic acoustic radiators is developed and applied to the design of a prototype which operates over approximately one half of the required bandwidth. The prototype transducer was built and the measured results are compared with those predicted by the model. Recommendations are made for improving the performance of both the prototype and the array required to meet the full bandwidth specified.

Sports are an important part of adolescent development and fitness. Although sports can be extremely beneficial, skill and ability varies greatly from one athlete to another. Teaching with acoustical guidance (TAG), also known as clicker training, has been shown to help athletes improve their skills in such sports as football, gymnastics and even the high jump. The present study compares the use of standard coaching and clicker training to improve accurate shot put technique for two female high school track and field athletes. In comparison with other TAG research, this study is a component analysis that isolated the use of the clicker to increase drill accuracy in the absence of verbal feedback for six component glide drills; as such, other TAG components were not evaluated. The results revealed no systematic effect overall, although a counter-therapeutic effect during the TAG condition was detected for specific drills and specific individuals. / Applied Behavioral Analysis

No / Hemp concrete is an attractive alternative to traditional materials used in building construction. It has a very low environmental impact, and it is characterized by high thermal insulation. Hemp aggregate particles are parallelepiped in shape and can be organized in a plurality of ways to create a considerable proportion of open pores with a complex connectivity pattern, the acoustical properties of which have never been examined systematically. Therefore this paper is focused on the fundamental understanding of the relations between the particle shape and size distribution, pore size distribution, and the acoustical properties of the resultant porous material mixture. The sound absorption and the transmission loss of various hemp aggregates is characterized using laboratory experiments and three theoretical models. These models are used to relate the particle size distribution to the pore size distribution. It is shown that the shape of particles and particle size control the pore size distribution and tortuosity in shiv. These properties in turn relate directly to the observed acoustical behavior.

No / Graded porous materials are of growing interest because of their ability to improve the impedance matching between air and material itself. Theoretical models have been developed to predict the acoustical properties of these media. Traditionally, graded materials have been manufactured by stacking a discrete number of homogeneous porous layers with different pore microstructure. More recently a novel foaming process for the manufacturing of porous materials with continuous pore stratification has been developed. This paper reports on the application of the numerical procedure proposed by De Ryck to invert the parameters of the pore size distribution from the impedance tube measurements for materials with continuously stratified pore microstructure. Specifically, this reconstruction procedure has been successfully applied to retrieve the flow resistivity and tortuosity profiles of graded porous materials manufactured with the method proposed by Mahasaranon et al. In this work the porosity and standard deviation in pore size are assumed constant and measured using methods which are applied routinely for homogenous materials characterisation. The numerical method is based on the wave splitting together with the transmission Green's functions approach, yielding an analytical expression of the objective function in the Least-square sense.

This thesis is concerned with the estimation of the acoustic source signal-bearing in the presence of a reflective surface. The method to estimate the bearing of the acoustic source is the cross spectral analysis of two microphones in which the characteristics of the acoustic source signal is preserved. The echo of the original time history is removed by an advanced signal processing technique, called Cepstrum analysis. This technique is successfully applied to remove the contaminating effect of echoes in the measured time history. The work described is divided into several steps. A computer program was developed to examine the effects of reflection and the behavior of the Cepstrum under different operating conditions using simulated signals. The algorithm was then adapted to process experimental signals acquired under laboratory test conditions. An improved liftering process based on the knowledge of the echo time was developed in order to make the method relatively automated. The results of the experimental work show that the Cepstral analysis can be both effective and efficient in removing reflected signals from convolved time histories and thus successful in correcting a bearing estimate contaminated by an echo. / M.S.

This study presents a basis for the analytical and experimental procedures as well as design techniques required in achieving adaptive structures for active structural acoustic control (ASAC). Test structures studied in this work included a baffled simply supported beam and a baffled simply supported plate which were subjected to a harmonic input disturbance created physically with a shaker and modelled by a point force input. Structural acoustic control was achieved with piezoelectric actuators bonded to the surface of the test structure. The primary focus of this work was devoted to studying alternative sensing techniques in feed forward control applications. Specifically, shaped distributed structural sensors constructed from polyvinylidene fluoride (PVDF), distributed acoustic near-field sensors constructed from PVDF, and accelerometers were explored as alternatives to microphones which are typically implemented as error sensors in the cost function of the control approach. The chosen control algorithm in this study was the feed forward filtered-x version of the adaptive LMS algorithm. A much lower level of system modelling is required with this method of control in comparison to state feedback control methods. As a result, much of the structural acoustic coupling (i.e. system modelling) must be incorporated into the sensor design. / Ph. D.

Since advanced composite materials generally experience coincidence at lower frequencies than metals when used in aircraft fuselage sidewalls, they may allow more transmission of airborne noise thereby requiring heavier acoustical treatments. A sequential design approach of addressing first structural and then acoustical design does not take advantage of structural/acoustical coupling. A simultaneous approach is expected to help minimize the total sidewall mass. This thesis uses numerical optimization to examine structural/acoustical interactions and compare the sequential and simultaneous design approaches. Acoustical performance is defined in terms of the infinite panel transmission loss at frequencies surrounding the coincidence region (1600 Hz - 12800 Hz for the panels studied.) Impedance transfer theory is used to predict the acoustical properties of a flat unstiffened anisotropic panel treated with a fibrous acoustic blanket, airgap, and limp-mass septum. Structural analysis is based on a fatigue damage resistance criterion. Sequentially designed treated composite panels exibit transmission losses 15 dB - 45 dB higher (transmitted pressure is 6 - 180 times smaller) than a structurally equivalent, equal-mass aluminum panel. Depending on the type of acoustic excitation (specific incidence direction or diffuse source) and the acoustic frequency considered, the simultaneous approach alters the sequential minimum-mass panel in order to 1) improve low frequency performance by raising coincidence frequencies, 2) improve high frequency performance by lowering coincidence frequencies, or 3) make the coincidence region as narrow as possible. Since these structural alterations require that more mass be allotted to the panel and less to the treatment, they only occur for strong structural/acoustical interactions (i.e. near coincidence.) The simultaneous design approach can achieve a moderate improvement (TL increased up to 10 dB, transmitted pressure decreased by a factor or 3) over a sequential design for a particular acoustic performance index, although computation time is increased and acoustic performance may be sacrificed in other regions. / M.S.

A one dimensional normalized model for the frequency response of the acoustic power transmitted through nonuniform materials is developed. Using the ideal mixture model to relate acoustic velocity and impedance, this normalized model demonstrates that the power transmission characteristics are completely determined using only a composition profile and the parameters defining percent variation in acoustic velocity and impedance. For purposes of comparison, an analytically exact solution for exponential tapers is obtained. / Master of Science

Shape memory alloy (SMA) hybrid adaptive composites are a class of materials which combine the strain recovery and elastic properties transformation capabilities of SMA fibers with the structural characteristics of advanced composite materials. This study utilizes the Rayleigh-Ritz method and finite panel acoustic radiation theory to investigate the use of SMA hybrid composite materials for adaptive structural acoustic control by active structural tuning. Analytical models are formulated considering classical laminated plate theory (CLPT) and first-order shear deformation theory (FSDT), to predict modal and structural acoustic response to incident low frequency plane wave acoustic excitation. The analysis is further developed to consider simply supported adaptive panels that are tuned by local fiber activation, such that a panel composed of elastically uniform sections can be evaluated in a piece-wise fashion. / Master of Science

This research project was aimed at investigation of speech communication issues in industrial noise environments where workers utilize hearing protection devices (HPDs). A controlled empirical study was conducted to determine the effects of several independent variables on speech reception and discrimination including: l). subject's hearing configuration (unoccluded or earplug, earcap, earmuff-occluded), 2). ambient noise intensity level (60, 83 dBA), 3). ambient noise spectral type (low, white approximation, high frequency), 4). speaker's voice level (63 or 65 dBA in 60 dBA noise, 82 or 88 dBA in 83 dBA noise), and 5). subject's hearing level (normal hearing, slight loss, or moderate loss) used as a blocking variable. Isophonemic word discrimination, with male-voiced word lists presented through loudspeakers in an anechoic field, served as the experimental task. Twenty-three males and twenty-two females participated in the experiment and a mixed-factors, partial hierarchical design was used for data collection. Analysis of variance and Newman-Keuls multiple-range tests were applied to the data. All main effects, with the exception of hearing level blocks, were significant, in addition to several interactions. These are discussed in detail and depicted graphically. One fundamental finding was that none of the hearing protection devices degraded speech discrimination (in comparison to an unoccluded condition) in the 83 dBA ambient noise level. In fact, the most protective HPD significantly enhanced speech discrimination in the high noise level. In the low ambient noise level, there was some reduction in discrimination due to the wearing of an HPD, but this effect is not of concern because HPDs are not needed at low ambient levels for protection purposes. From the results, it appears that properly selected HPDs can be expected to at least maintain speech discrimination levels (equivalent to unoccluded levels) in moderately-high intensity industrial noises of varied spectral characteristics. / Master of Science